1. Field of the Invention:
This invention relates to heat exchangers and more particularly to modularized construction therefor and associated tube bundle module-shell support members.
2. Description of the Prior Art:
Alternatives to conventional power generation schemes have been sought in recent years. A concept called Ocean Thermal Energy Conversion (hereafter referred to as OTEC) has, as of late, been thoroughly evaluated as to its feasibility in commercial applications. OTEC generally utilizes natural temperature differences (as much as 40.degree. F,) between ocean surface and subsurface waters to develop a pressure difference across a turbine through which a vapor is expanded and whose expansion energy is converted to mechanical energy for rotating a generator.
Open or closed cycles utilizing the OTEC power generation principle can be utilized to advantage under various circumstances. Closed cycle OTEC systems require isolation of the primary, expandible fluid from the environment and thus necessitates the use of heat exchangers for the motive fluid to absorb heat from and reject heat to the relatively warm surface waters and relatively cold subsurface waters respectively.
Due to the small temperature differences available for heat transfer, extremely large evaporators (vapor generators) and condensers are required. To effectively separate the ocean water from the motive fluid shell and tube heat exchangers have been selected and have been identified as the most costly pieces of capital equipment utilized in closed cycle OTEC systems. Development of a cost effective heat exchanger design is absolutely essential if an economically viable OTEC power system is to be achieved.
The major problem areas for developing extremely large shell and tube heat exchangers were fabrication and welding problems, high cost of alignment and special coordination of large internal parts, shell assembly, and tube insertion on the ship to be used for OTEC, supplying uniform motive fluid distribution with a minimum of nozzles, and obtaining suitable tube supports for preventing tube vibration failures. After considering the aforementioned problems and investigating their solutions by utilizing conventional power plant heat exchanger practice, it was decided to lower cost shop fabrication (compared with field fabrication), fabricate parts and subassemblies which are commercially shippable, and develop liquid distribution and collection systems for the heat exchangers' shell side that are less costly than previous designs.
A modularized unit for use in heat exchangers was illustrated in U.S. Pat. No. 3,595,310 which issued July 27, 1971. Such modular unit utilized tubes embedded within pervious metal but can be very costly in their manufacture and result in extensive field labor insertion. U.S. Pat. No. 3,986,549, which issued Oct. 19, 1976, illustrates a modularized gas-to-gas heat exchanger support structure. Such support structure does not, however, suggest how to support the actual heat exchanger surface within an enclosing shell member.